UNDERWATER SEARCH is used for:
– search of sunken objects
– search for drowned people
– inspection of underwater objects
Divers are often faced with the need to find something underwater. And newcomers genuinely wonder why it is sooo difficult to find when you were clearly shown that “it sank right here!” 🤦🏻♂️
If your beloved phone went “like a stone to the bottom”, it means “quickly”, but not “downward”. Even in the absence of current, objects sink along a bizarre trajectory and very often glide far to the side. And if there is a current, then both the drift and the possibility of dragging along the bottom must be taken into consideration. Also keep in mind that objects at the bottom create turbulent water flows around them. And this washes them into the ground: sand, silt, gravel. And the more the object rises, the stronger the turbulence and the faster it is washed out. Therefore, it is important to start an underwater search as quickly as possible!
Underwater search requires detailed planning, patience and perseverance. It is very rare that a search can be successfully completed in a short time. If the search underwater area is large, but the target is small, the search under water may take a long time.
As with any dive, effective underwater search requires a thorough dive plan, namely:
1. Have a clear description and understanding of what / who we are looking for
2. Clearly define the search area
3. Choose an underwater search method
4. Determine the required number of divers
5. Determine how to raise the object to the surface
6. Prepare and take with you all necessary tools and equipment to search and lift the object.
SEARCH AREA AND DIVE PINNING
Maps, documents, eyewitness accounts and common sense are used to determine the underwater search area. Experience shows that the most unreliable source is eyewitnesses. It is difficult to visually fix the exact spot on the water. In addition, it is difficult for the human eye to determine linear distances in the water area. Therefore, the most practical way to fix an underwater search location is to determine the alignment. Thus, you will fix the underwater search line, and if you define two alignments, you will have a point. If possible, place a buoy or determine GPS coordinates. This will make it possible to quickly get into the area of underwater exploration in case the search takes several days.
It is wise to start an underwater search while you are on the surface. Here it is possible to move at high speed, devices for scanning the bottom from the surface are at your disposal: echo sounders, sonars, magnetometers, ground penetrating radars, etc., an autonomous air source is not required. The devices will allow you to quickly survey the bottom in large areas if you have them and you know how to process the information received.
If there are no devices or experience with them, then an aquaplane can be used to cover a large area of underwater search with good visibility. The diver holds onto the aquaplane attached to the motor boat and adjusts the depth of the dive. The boat is tacking, covering the search area. When the diver notices something interesting, he simply let go of the aquaplane. The boat returns to the diver and fixes the location. GPS receivers make this easy.
CHOOSING AN UNDERWATER SEARCH METHOD
Once the underwater search area has been determined, the next step is to select a direct underwater search method. Here are the most common ones:
COMPASS SEARCH
The direction of underwater movement is selected by the compass, the distance traveled is calculated by the number of strokes of the fins. It’s easier to count strokes of one leg. Following a square on a compass is not difficult. But, if you spend some time before diving and write an algorithm for the trajectory of expanding squares on your tablet, you will be able to search for a large enough area under water. The main disadvantage of this method is its low accuracy. Your error in passing each straight section (both in length and in direction) will accumulate, and at the finish can be quite significant. This underwater search method is ideal for finding large objects with good visibility.
CIRCULAR SEARCH
makes it possible to examine the water area in more detail. A well-moored buoy is placed in the center of the search area. An end with measured markings clings to it, for which the diver holds at a certain distance. Having made a full circle, the diver releases several meters of the end, thereby increasing the search radius, and again goes a full circle. The amount by which the radius is increased over and over again depends on the visibility and size of the sought object, and should be less than the visibility. To speed up work, several divers can hold on to the same marked end at a certain distance from each other. If there are no characteristic objects at the bottom that allow you to visually assess the passage of a full circle, a radial line must be laid before starting the search. If a radial line is used, it is necessary to make a dimensional marking on it, according to which the diver will increase the search radius circle by circle.
This method gives good results when searching over large areas in conditions of low visibility and no currents. But if the radius is more than 30 m, then the stretching of the rope makes it difficult to effectively circle underwater search. The center of each underwater circular search must be marked very carefully! Unlike squares, circles don’t overlap as well. As an alternative to circular search, you can use a semicircle or a specific sector search.
LINEAR SEARCH
requires laying a baseline at regular intervals. This line is bled directly off a moving vessel following a clear course. The baseline is vented at speed to be straight and taut and must be flooded and secured with buoys at each end. The base line can reach thousands of meters in length, this is limited only by technical capabilities. If desired, several parallel lines can be set if the search area is large.
A group of divers (at least three, possibly more) descends to the baseline, taking with them a search line, the length of which depends on the number of divers and visibility under water. Divers position the search line perpendicular to the baseline so that the same number of divers are on each side of the center diver (operator), directly above the baseline. The distance between divers should be such that there is an overlap of visibility from neighboring divers.
All divers hold the search line with both hands. Once the divers have reached the starting position, the operator signals the start of the search by pulling the rope with both hands. Each diver repeats the signal for confirmation and passes it on to the next. Thus, the search line moves forward regardless of the length, and the operator maintains a position above the baseline. Each diver examines the bottom and, having noticed something interesting, stops the movement with a signal, marks the find with a marker and gives a signal to continue moving. When the entire area around the baseline has been surveyed, the underwater search is repeated on the next parallel baseline. The distance between the baselines should assume an overlap from the already explored underwater area.
This method is good when the underwater search area is stretched along a specific line. The presence of a large number of divers with good visibility allows you to survey the required area in one pass. But the effectiveness of this method requires the well-coordinated work of the entire group of divers, and especially the ability to work with the signal end.
NETWORK SEARCH
involves limiting the search area with ropes around the perimeter. Very effective as the markings are applied directly at the bottom, but it takes a lot of preparatory work, as well as ropes, weights, buoys and experience. A permanent grid is set inside the perimeter, the size of the squares of which depends on the visibility and size of the desired objects. This method is good for underwater search for relatively small objects and for archaeological excavations. The web based underwater search method ensures you view every square inch of the bottom
JACKSTAY SEARCH
stands out as a simplified version of the network. In this case, jackstays are laid along the two long sides of the perimeter. The ropes have a dimensional marking, and a running end is pulled between them. Underwater search begins from one end of the ropes, the running end, according to the standards, gradually moves to the other end. In this case, much less ropes and preparation time are required.
All of the above methods of underwater search have many variations depending on the search conditions, equipment availability and the number of search divers.
The purpose of an underwater search is to lift something out of the water to the surface. Remember: the longer an object has been under water, the worse it will stay its appearance to the surface. When starting an underwater search, you need to know how to lift and/or preserve your finds. And before you raise anything to the surface, make sure the legality of your actions.
I wish you successful dives and under water searches!
